The present invention relates to a keyboard apparatus, and particularly relates to the keyboard apparatus used in an electronic musical instrument constructed to impart a dynamic reaction to a finger action to thereby improve a key touch. More specifically, the invention relates to the keyboard apparatus provided with a mass member such as a hammer arranged to produce good key stop touch. Further, the invention relates to the keyboard apparatus constructed such that key members are well fitted into a support to provide good operability of the key members.
U.S. Pat. No 4,901,614 discloses a conventional keyboard apparatus having a hammer linked to a corresponding key. In the conventional keyboard apparatus, the key is pivotably supported at its rear end portion by a keyboard frame. A free front end portion of the key is depressed by a finger action so that a contact portion of the key abuts with a side face of the hammer to depress the hammer in linked manner to the key. The contact portion is disposed downward on a side of the key at a lengthwise intermediate portion closer to the rear end than the front end. The hammer has a rear end portion pivotably supported by the frame, a front free end portion and an intermediate contact portion which is depressed by the key. In such a construction, a distance from the rear end portion to the contact portion is set smaller than another distance from the free end portion to the contact portion so that the free end portion is accelerated in the pivotal movement of the hammer to increase a load resistance thereof to create a heavy key touch. Such an acceleration mechanism can efficiently create a relatively heavy key touch by a relatively small weight of the hammer. Therefore, the keyboard apparatus having such a hammer can reduce an overall weight and can improve a dynamic key touch upon depression, as compared to another keyboard apparatus having a static weight attached to the free end portion of the key instead of a dynamic hammer. The dynamic key touch is a dynamic reaction received by a finger dependently on a depressing strength of the finger. The dynamic reaction is increased as an inertial moment of the key and the hammer is made greater. The inertial moment I is represented by I=m.multidot.r.sup.2 where m denotes a mass disposed at one end of the hammer, and r denotes a distance from a pivot center to the mass. The longer the distance r, the greater the inertial moment I. Accordingly, the hammer is pivotably disposed within a given space of the keyboard apparatus while a fulcrum of the hammer is positioned far from a mass center of the hammer, i.e., a center of gravity, thereby creating a heavy and dynamic key touch likewise an acoustic piano instrument.
Such a type of the keyboard apparatus having the hammer is provided with a pair of separate stopper means. The one stopper means is placed in direct contact with the key to fix upper and lower limits of a stroke movement of the key, while the other stopper means is placed in direct contact with the free end of the hammer to limit a stroke movement of the hammer. Further, the conventional keyboard apparatus is provided with guide means which is engaged with the free end portion of the key to vertically guide the stroke movement of the key while preventing a torsional displacement and a lateral swing of the key. The guide means is comprised of a guiding member elected on the keyboard frame and inserted into tile key in slide contact with opposed inner faces of the key to linearly guide the same along the vertical direction.
However, due to the above mentioned angular acceleration mechanism, the hammer stroke is normally set three times as long as the key stroke. Consequently, a gap between upper and lower stoppers of the key is significantly different from another gap between upper and lower stoppers of the hammer. It is difficult to match positions of the key stoppers and the hammer stoppers with each other. For example, if an effective position of the key stopper is shifted by 1 mm, a corresponding effective position of the hammer stopper must be shifted by 3 mm. The key stopper is composed of a felt or else which deeply sinks when the finger strongly hits the key and which shallowly sinks when the finger weakly hits the key. The hammer stopper is also composed of a felt or else which must sink three times as much as the key stopper. The hammer stopper must have a sufficient and accurate thickness to absorb a variable sink amount dependent on the strength of key hits. Therefore, accurate work is required for production of the components and assembly of the keyboard, such as the key stoppers and the hammer stoppers must be positioned in matching with each other, resulting in bad production efficiency and cost-up. The key stoppers and the hammer stoppers may be positioned discrepantly relative to each other, hence the key stroke is made inaccurate to cause incompatible key touch.
There is another drawback as to the compatibility of the stopper members relative to other parts in addition to the above mentioned drawback of the positional discrepancy among the stopper members. For example, the keyboard frame may have a structural distortion which may cause an erroneous alignment of the stoppers even if the felt material thereof has a proper thickness. Consequently, a stop position of the key may be offset from that of the corresponding hammer, thereby causing an incompatibility of key touches at the start or stop of the finger action. Particularly, if a positional error exists at the lower stoppers which limit a downward stroke movements of the key and the hammer, the hammer may bounds to vibrate at the key depression. Such a vibration may generate a noise, or may be transmitted to the key to generate an incompatible key touch.
In order to remove such an ill vibration of the hammer due to inaccuracies of the keyboard assembling and the parts working, a spacer tape may be attached to a vibrating portion. Otherwise, a total thickness of the felt of the stopper may be excessively increased to absorb the vibration. However, such a treatment further complicates the assembling work, and otherwise hinders a firm key touch at the stoppage. As an alternate choice, a defective keyboard frame may be provisionally eliminated to avoid ill vibration of the hammer. However, such a treatment would raise a total production cost of the keyboards.
In addition, dislocation of the stoppers may emerge as the time passes. Normally the hammer stopper can be correctly positioned relative to the key stopper just after the assembling work. However, after repeated stroke movements up to several thousand or several ten thousand times in a long period of the practical use, the lower stopper of the hammer may suffer from a permanent compressive deformation beyond an elastic limit. Further, the upper stopper of the hammer continuously receives an upward bias from the hammer so that each stopper is variably deformed by an aging effect dependently on a stroke frequency of each key. Consequently, the hammer stopper becomes dislocated from the corresponding key stopper to thereby generate the incompatible key touch and the ill vibration of the hammer due to bounds at the stopper.
Aside from above, as disclosed in the U.S. Pat. No. 4,901,614, the conventional keyboard apparatus is provided with the guide member which is inserted into the free front end portion of the key, and which has an extremely elongated shape in the vertical direction. Such a guiding structure may increase an overall thickness and a total weight of the keyboard, and may complicate an internal construction of the keyboard. Particularly, a front part of the keyboard is made thick so that a space between the keyboard and a player's knee is tight, thereby hindering operability of the keyboard when the player sits in front of the keyboard. Further, in the conventional keyboard apparatus, the key is supported at its rear end pivotably only in the vertical direction to allow the stroke movement. In such a support structure, the guided free end portion is occasionally not aligned with the supported rear end portion when the key is assembled into the frame. Such a misalignment may cause an ill play of the supported portion to generate a noise, or otherwise may impose a subsidiary stress to the supported portion to shorten the life of the key.